I have taken that mindset & pray constantly for strength. I've given up on the idea of an "intimate" marriage & I hold no resentment toward my wife. I still treat her like God intended & don't expect anything in return. My only goal is keeping her happy while I suffer in silence.
I don't think the way to love one's wife is to give without expecting anything in return. Did Jesus do that? Did God forgive us and ask nothing in return? He asked for everything in return, our whole selves.
As a married man, your responsibility is to be like Jesus who washes the church with the water of the word, presenting her blameless. You should desire your wife's sanctification. Part of sanctification for a married women is obeying I Corinthians 7 and having sex with her husband. So you should keep up the sex.
Take the duty sex. I know dry passionless sex leaves a lot wanting. But keep up what level of intimacy she'll give.
Don't give up either. Encourage yourself in the Lord. Then, as the head in the marriage, keep pushing for a better marriage-- more long walks on the beach if that's what you think you need, or more couple time. All that sort of stuff to build up the relationship. Pull rank if you have to. You can tell her I'm the head in this relationship and the Bible teaches you to submit to me, and I am responsible before God for how I treat you as a husband. I see that our marriage has a need for X, Y, and Z, so I'm going to schedule some activities. Tell the mother of that baby your wife can't babysit on certain days, and schedule a date for your wife. Tell her what to wear and plan the whole thing. Or spend some alone time talking. Take the lead in fixing the stuff. If she doesn't go along with the Biblical headship role, you may need to be more subtle about it. Some women say they don't like the man being in charge, but something about it is attractive to them on a more primal level, which is something to keep in mind.
Speaking of that, in the bedroom, if you can still pick her up, before you do have sex, do something different-- pick her up and carry her over the threshold. Pull her into the bedroom for a kiss. As long as she's having a good time, you can be physical like this and experiment and see if something like that appeals to her. You can also show a lot of physical affection during the day, hugging, patting, squeezing, groping if no one is around, as long as she responds well. Act like a newly wed, and maybe it will rub off. If you've been separated, you may have a good excuse for acting a little wild when you get her alone. If you push her limits a little with the affection and she acts indignant at sexual attention, "You stop looking so sexy and I'll stop..." doing whatever. Hopefully, she'll smile or laugh at that. If you up her passion for her 10x while you are having sex with her-- act like you just want to devour her, if only 10% of that rubbed off on her, that would be an improvement.
Or if you haven't been all that romantic, you can try the flowers and songs under the window approach. I know at times, I sure have wished my wife would have been more passionate about sex, but I didn't realize I wasn't providing the proper context. Right when we got married, we had a lot of sex. Many years later, we didn't have as much. But I remember, right when we got married, I might grab her as soon as I got home, give her a passionate kiss that said I have to have you now, and pulled her to the bed. And she was into it. Eight years later my approach was, "Do you want to have sex tonight?" And she might say, "no," and then she might say no, and that could turn into a disagreement. I'd just left it open for her to say 'no' by asking her the way I did, especially in my matter-of-fact, unpassionate, unromantic way with no warm up. Why would she want sex? If I'd been kissing and hugging her for four hours, and I picked her up in my arms and took her to the bed, making her heart skip a beat, I'd increase my chances of her having some desire. It's kind of like selling a used car. If the salesman acts like he doesn't think you'd want to buy it, you probably won't. But if he acts like he knows you will want it, you might be more inclined to buy it. She may feel more attracted to you because of the combination of passion and confidence.
Be careful with the picking her up thing if she's gotten heavier and you aren't as strong as you used to be, though.
If you act like the passionate strong man that must have her, or the sappy romantic guy who loves her so much...or whatever else pushes her buttons, you might get a little more willingness on her end. We don't watch much TV around here, but we did watch one show a while back. I asked my wife what she thought of the leading male characters and how attractive they were. It was insightful for me regarding what kind of personality traits she found appealing in a man. If she likes the decisive tough guy, do that in the bedroom. If she likes the soft, romantic guy, use that approach. A lot of American men err on the side of being to sensitive and romantic because that is what women say they want, but women say that, but in high school, a lot of the girls were attracted to the tough guy jocks who teased them mercilessly and didn't open the door for them.
I think the separation thing is a bad idea. She's not cheating on you, beating anyone, or anything like that? The issue is a lack of passion, right? If her heart has grown cold to you, I wouldn't risk absence making the heart grow fonder. My guess is you'd have more success 'tightening the leash' rather than loosening it. (I know, it's an awful metaphor.) I suspect you'd have better results trying to really manage the relationship.
And don't forget about the spiritual side. I've heard that less than 1% of couples who pray together regularly get divorced. You can pray about feelings and passion in the marriage, too.
