Hi, I'd like to help you with your questions.
It sounds like you are on the right track with the relationship. But there are some concern over how he is handling the relationship so far. For one, he is in a relationship right now and is also with you twice a week and each weekend. You have been together for 5 weeks. This is something to pay attention to because it could mean that although he is a great guy, he might have a problem with staying faithful. People do meet others outside of their relationship and leave, but if he has done this before (like during his marriage), it may show a pattern you need to be aware of.
It might be a good idea to wait to get to know him better before you to open up emotionally in the relationship. Meet his children, spend time around him with his kids and get a better idea of how he treats his ex, his family and his friends. This will tell you a lot about his character. Also, your idea of taking this slow is good. It is easy to get caught up in the excitement of a new relationship and forget that you want this to be a long term (hopefully forever!) relationship. In order to be sure before you invest yourself, try watching what he does as if you are not involved with him, like an objective observer. It can help you have a more objective view and better judge what you see. This will help you see if he is real and serious about his feelings for you. Also, tell your friends and family about him and let them meet him. They can also help you see things about him that you may not be able to see right now.
Also, see how he handles the problems in his life. When something goes wrong, does he approach the problem by thinking it through or does he fly off the handle and get upset? In other words, is he quick to anger? Here are some other points to be aware of:
Does he seem dependent on others or does he handle his own life responsibly?
How does he seem with his money? Is he too generous, or does he seem unwilling to spend his money even for items that are needed?
Is he always thinking of others or does he talk about himself a lot?
Is he moody or does he seem laid back and easy going?
What attracted you to him? Does he still seem to have this trait and does it seem genuine?
Once you get a better feel of who he is, then you might want to let him know how you feel. The best way to do this is to tell him. Be honest and open. Let him know that as you have gotten to know him, you find you would like a relationship with him. See what he says. If he responds well, you can see if he is willing to have a monogamous relationship. Then let things develop from there.
I hope this helps you,