I love what "momofmany" had to say. However, I don't think you should stay together because of the kids. At this age, the kids are resilient and can adjust. It's easier to make changes now rather than later.
With that said, though, it's more important to get counseling and try to work on your relationship with your husband. We're a society that throws something away when it's broken and just buy a new one instead of fixing the old one. It's a bad, lazy way of handling things. Being married is a lot of work! Don't throw it away because it's broken. Try to fix it.
Plus, with 3 kids under 4, it's no wonder you and your husband are having difficulty, that you've lost the loving feeling. The demands of raising kids, financially and emotionally, is very draining. You are exhausted being with them all day and having the responsibility of feeding them, doing laundry, cleaning house, nurturing, etc. Plus, when you're at home, you don't get a release for you or other adult stimulation. Your husband is exhausted working and having the demands of supporting a family of 5. He needs to unwind when he's home and release the stress of work. This doesn't negate his responsibilities helping at home, but your relationship should not be based on who's going to take the trash out and when. Marital problems are typically caused by both partners, not just one. Take responsibility for it yourself.
So, DO NOT GIVE UP until you've tried everything to make your relationship work. You reap what you sow. Work at it! Try counseling! It works! Read books like "The Proper Care and Feeding of Husbands" by Dr. Laura Schleinger. Validate your husband and all that he does. Have "date nights" that stimulates your relationship before kids, which means no talking about the kids or housework. Talk to your husband about his day and about his work. Listen to him. Find ways to put that "spark" back into your relationship and regain the love you once had for your husband. It's still there; it's just muddled with the demands of family life.