Should I tell him how I feel?! #heartbroken

Ok please someone help me out here...

I've been "with" this guy since February and have been serious about him and assumed the feelings were mutual even though nothing offical had been said (I know... stupid). Anyways I was last with him last sunday morning and we were at a motel and I had the strongest urge to tell him I wanted something more and that I wished I had said yes to when he asked me out 3 years ago. I didn't say anything though because we were both pretty fucked up and I didn't think it was an appropriate time. Two days later he messages me asking me not to tell anyone we were together especially a certain girl. I start freaking out on him and he was genuinely confused why i was mad and upset. Now it's been a week since that and I can't stop thinking about what would've happened if I had told him. Do you think I should still tell him? He's not dating her and has only met her once in person. I can't stand having these "what if" thoughts. I can't sleep. He's asked me to get a place with him in the past (recently) and said that we're getting married if we're both single at 30. I rejected him a few years ago and have always thought maybe that's why he never tried again...

UPDATE:

I told him this morning and it didn't go as I hoped at all 💔 and he's expecting me to lie to this girl about us since she messaged me today. I want to tell her so bad but it will ruin my friendship with him.