I think that the quality of relationship and satisfaction vs disappointment ratio in your relationship with your yf will depend a lot on how much time you get to BE with him.

I think the time factor is imperitive.
The reason I think this is that, more than anything, as a BL, I simply want to BE with my yfs. It would make relitavly little difference what was going on during that time but if my yf was with me and wanting to be with me... paradise! I suppose others could relate to this.

Sure a relationship with any real person is very much different than our ideal imaginings... one of the unexpected things for me is how much I mess things up: say the wrong thing; miss oppertunities to affirm him; respond poorly to his enthuasium etc... when they are the very opposite of what I WISH for.

I encourage you to take a more positive outlook than "it'll only be downhill from here-on". Sure certain things will go down hill ... like his boyish looks. But other things will hopefully improve exponentially... like his maturity and ability to care for you and be a solid friend to you... his ability to engage in conversation... the attachment you feel towards each other etc...
If you endure and stay committed and God blesses you with oppertunity to continue the relationship long term, I feel pretty sure the positives will well outweigh the negatives.

Blessings
Cat.