Let me understand this: You have been dating for nearly a year and neither of you has mentioned "love" or discussed the future?
When you mention seeing him with his ex, please explain how and why he's seeing her.
Did he end things with her shortly before starting up with you?
Thank you for your patience. It seems that you are a very patient person in ALL areas of your life. Nearly a year with a gentleman and no mention of love or advancing the relationship? That might be considered "too" patient.
--- There may be one of a few things going on here. First, I suspect more than anything else, that he may be going off with other 'friends' and not talking about making what you have 'official' because he's concerned that he'll be rejected.
That talk you had recently that made you feel better? It's time to continue that. It's time to come right out and say to him what you've said here.
Tell him, "John, because I trust our friendship can handle this and I trust you, I'm going to speak my heart. I am not 'developing' feelings for you, I've got them. They are there. And because they are there, when I see you go off with Mary and her friends without me, it hurts. Mostly because I'm not sure how you feel. So, here's your chance to get those pesky feelings out in the open" (keep it light, don't scare him)
--- If he says he doesn't feel 'that' way about you, thank him for being so honest and assure him that you will be working at reeling your feelings back in. That nothing should change between you.
Of course it will, but in time there's a chance it will go back to what's been working for the last 11 months.
And you will know for sure that keeping you mind, heart and options open in case someone else comes along is the right thing to do.
But the botXXXXX XXXXXne is that you must trust him and what you have right now, enough to be honest. Right?