asking my husband for a separation

My husband has had an affair and this is the second time this has happened. The first was over ten years ago and he was very remorseful at the time, telling me it would never happen again. Now I am at a very low point and I'm struggling to find the motivation to stay with a man that I cannot trust. I have asked him to leave the house for a couple of months so we can get counseling and sort this out. He refuses to leave, saying it is his house too. I feel it is reasonable to ask for this time apart but he says I am unreasonable.
I'd be interested in know how others in this same situation have handled it.

First, I haven't been in your situation...and it grieves my heart to know that you're going through it. Second, because I know almost nothing of the complete context, I'm going out on a limb to respond...it could be way off the mark in terms of "correctness" or helpfulness. Third...forgive me if it turns out later that I'm wrong.

An initial response I'd like to give is that he has already separated himself from you in some way...and perhaps you have done the same. He has stepped away from the marriage vows that you both took, and for what ever reason, wants to be able to continue the way things are.

Having established that separation/divorce of a sort has already taken place, the choice to physically leave the premises is an intensely personal one, and probably no one can fully understand how you feel or what you need. I can't tell you to leave or stay...you'll have to decide. What I can see is that there is that the relationship is broken, and needs healing. This almost requires an outside "mediator" to observe, listen, and try to suggest avenues of healing. Clearly this "mediator" must be one who shares your world view, is very wise, and is well qualified to actually help, not just listen. Whether or not it is reasonable for your husband to leave or for you to leave the house is not so much the point as, "Will he enter into counseling with you to try to choose a path that will restore the relationship." If he won't, then it seems reasonable to leave the premises with the understanding that (a) lack of demonstrated interest in reclaiming the relationship and (b) failure to recognize and admit the damage done by the affair are indicators that he no longer values the relationship as he should. That being the case (if it is indeed the case), until he does, it seems reasonable for you to say the following; you choose not to be around him, will not share your bed with him, will not continue a financial partnership with him, will not live in the same location, and will not place further trust in him. If that is "ok" with him, then the relationship is essentially over; if it brings "Godly sorrow" to him, and he turns away from his path of emotional separation/divorce, then the long road to restoration can begin...and each of you needs to "bring your checkbook and workboots" to the task.

In thinking all this over, please remember that it frequently takes time (lots and lots of it) and consequences for people to fully grasp the situation...and determine that they want "to leave" or "to stay". As best you can, whatever you decide about the "separation" idea, please give much prayerful time for each of you to determine the path that you will take...even if there are some legal measures taken in the interim. Remember that, as we are all individual "restoration projects" to our Creator, our relationships (marriages included) often require the same type of restoration...and that such a project requires time...commitment...perseverance...and divine help. Blessings to you in the path you choose.