Partner, 26M and me, 28F. Opening our relationship. I have serious reservations about two things.

So my partner and I had off and on problems over the past year around the question of opening our relationship (not poly). I've been resistant and we've had a few false starts but I finally recognize that this is important for my partner's growth and I've decided to try it and see where it takes us. There are two issues:

• While still in a monogamous relationship, he kissed another woman a couple weeks ago. This gave him a lot of perspective on his need to open the relationship. However, I feel betrayed and wonder if I can trust him and doubt this is a constructive way to start the open relationship. Thoughts?
• He says he's don't know yet if we have a long-term future together (though he says it's a possibility). That he wants to be with me and he loves me (and we had planned a move together to another country) but he can't guarentee I'm the person he wants to spend his life with (we've been together two years). I don't think he's using the open relationship to replace me, but it could happen if he's not committed to me in the long term. Like what can I hold on for for security?