You mention that GALing would not make a huge impact.
Are you saying that you may have been too distant? Is this one of his complaints? If so, have you tried a 180 and pursued him? Asked to be with him when he was doing things or simply being around him and chatting... vs. trying to make plans to do things with him.
What about asking him to make plans to do things with you where he is in complete charge of everything?
You slipped. A dating site may have been inappropriate. There are other ways to connect with people and often I have seen it suggested to choose people of the same sex (or opposite, in the case of gay Ms). Now, you may have to consider that you will have to regain some trust, there.
OTOH, he claims that is the nail in the coffin. It is likely just a reason and it could have been any other reason. That one may have just conveniently dropped on his lap.
You CAN change things. You can change you.
Did you make notes when you talked to the coach? Go over some of the things that were discussed. Rather than the specifics, what were the "themes" that really stood out with the coach?