If we don’t have marriage in heaven …. And we all have mansion/rooms in heaven, what is the point of living alone? It would seem kind of lonely being alone in your own place, although that emotion wouldn’t exist.
Let’s clear up a couple of misconceptions you have picked up. First, do you think God would go to all the trouble He’s gone to so you can have a place in His kingdom just to make you feel sad in some lonely mansion? Paul said the life He’s prepared for you will exceed your current ability to imagine it (1 Cor. 2: 9). In ages yet to come it will stand as His demonstration of the incomparable riches of His grace, expressed in His kindness to you in Christ Jesus (Ephes. 2:6-7). Think of the very best thing you can imagine God doing for you, and then realize you’re not even close.
We make a big mistake when we think of our next life as just a different version of this one. We think if we don’t have all the things we have here we couldn’t possibly be happy there. I believe the reality is that if He told us exactly what He has in store for us, we wouldn’t be able to stand the life we have now. And yet, because we don’t know, we wonder if it will be as good as this one. Believe me when I tell you it will be so much better, it will be like walking out of the blackest night into the bright light of the best day ever.