Hook certainly loved Milah, the tattoo is proof of that. I don’t think that necessarily means that they won’t have him fall in love again though. Milah may have been Killian’s one true love, but he became a whole new person after her death, so they can give Hook a true love too.
I’ve been thinking a fair bit about the prospect of Hook and Ariel recently, and have come to really like the idea. Sort of decided that I want there to have been a rivalry between King Triton and Davy Jones, and then one day Triton’s daughter falls in love with Davy’s son in Neverland and because her father forbids it, she has to make the deal with Ursula to be with him, and they’ll have a grand old forbidden romance.