He does love him. Actually he admitted his feelings already. Misaki is just having troubles adjusting to the relationship..
And keep in mind that Misaki was straight before he met Usagi. It will take time for him to really get used to being in a gay relationship.
Four years of a relationship is not enough time? Nah, it is just stretching things out a little too much in my opinion. Sensei should have just adjusted the time period if that was the case. Misaki may have said it once, or twice, but he still protests any physicality as well. If you don't know your own mind after four years, then something is wrong. But that is just my opinion. Akihiko even said that he has not grown.
Believe it or not....4 years in a relationship is not long at all especially if it's a relationship where you start from where Misaki is coming from....
Perhaps, it is all a matter of perspective I suppose. I would think that someone would be able to acknowledge their feelings after a certain period of time. I know that this is a plot device, but it can grow a little tiresome at times. I have a relative who got married a month after meeting her husband, they moved to a different country and just celebrated their 50th wedding anniversary. I know that it can take time to sort out your feelings, but four years of cohabiting and having sex and still unable to acknowledge your feelings just seems to push the boundaries.
A boat trip around the world that only takes one week? That is one fast ship! And, hate to say it but Misaki is getting annoying, his refusal to acknowledge his feelings for Usami is just too unbelievable. If he does not return Akihikos feeling, he should stop living with him and stringing him along. Four years is more than enough time to grow p and determine how yo feel about someone. Just saying.