Think

as in

"I think I love you."

Variations: "I think we’re good for each other ... I think we should spend more time together ... I think we are drifting apart ... I think it’s over."

Obviously he’s not actually "thinking". If he was - if by chance some scrap of his grey matter was genuinely in working order - he wouldn’t tell you that, which is hedging his bets and demeaning, but say straight out either "I love you" or "It’s all over." (Delete one or the other depending on where you are in your relationship.)

In the early days, when all is going well, "think" serves two clear purposes for him. First, it expresses his amazement at the situation he finds himself in - that he, great as he is, actually might like you, despite what he sees as your flaws. Second, it offers him an escape clause in case you decide to reject him (even he will have moments of insight when he realises that this is a possibility) or in case he decides the whole thing isn’t such a good idea after all. How easy for him then to take refuge in the memory that he didn’t actually commit, he was only "thinking" about it.

In the latter stages of a grand passion, the word acquires a completely different dimension. Of course, once again, he is not actually "thinking".

If he has ever bestirred himself to take the relationship that seriously, it was weeks before - a few fleeting moments of cogitation while he was stuck in a traffic jam perhaps or a bit of mental probing during a lull in some match. Whatever, now his mind is made up but his courage is lacking. Cringing, he is
offering you a chance to do all the hard work, to say, "I agree, we should finish." So he can say, "Oh, right then."

There is one other possibility. He may be worried you are tiring of him and testing you. You can’t expect him to simply ask, could you? That would be too simple. Easy response in all cases: "Don’t think. It doesn’t suit you." Alternatively, tweak his ears and ask him how much longer is he going to keep you in suspense before he might actually "know" what he feels?