Hi. Being alone for so much time allow someone to get into very niche hobby and time consuming routine. It may be that he tossed it away for a while to make room for you or squeezed some of his normal activity to a minimum hopping he could fit all in his schedule but it did not worked.
The only way you could really know is to ask him for a proper post mortem of what was the problem so you can effectively move on. It surely is a problem from his side and not yours. At that age men start to reconsider a lot of things (project and dream) and plan the rest of their life accordingly. Perhaps he love you enough to know you will not be happy with him if he can't reach a certain monetary comfort level or that he will not always to invest enought time with you. He may also lack time alone with himself (often the case with introvert as they usually do fine hermit).
If he really is done with you, he should have no fear or reason to not tell you the truth.
"Almost" three months of dating once a week isn't much to think about building a permanent relationship on, especially for a 42-year-old man who has never been married. That's only about a dozen dates. It sounds like he just tested the waters and decided he wasn't ready for a permanent relationship at this point in his life. The only way to know for sure is to ask him. However, it sounds like he has made up his mind after giving it a fair trial. I would take his advice and move on. It's a shame that things didn't work out.
I'm so sorry about that.
I don't blame you for being confused. For some reason he changed his mind. Without his input there is no way to know why. Perhaps the idea of something permanent scared him off. I hope he will tell you something to help you understand what happened. Most people do manage to have both friends and intimate relationships as well. Perhaps he just hasn't figured out how to do that. Such a shame.
As requested I have opted out although as a nurse practitioner I counsel people every day. I'm sorry I'm not telling you what you want to hear. The question is open to any expert.
You say he mentioned he find hard to plan every weekend and have time to still see his friend. That is exactly what i was mentioning that someone used to be single around that age struggle with: not enough free time slot in his routine (and that routine can get pretty fat with years).
You can still win him but you will have to let him a lot of freedom and not plan much early on. If you can sell that to him that you would still be happy that way, over time he will slowly remove older routines progressivelly (like someone that slowly quit smoking).
About why he was planning in advance trip and such, it may have to do with him already doing trip in his routine and being with you at that time is not harder to schedule. You may also look around him if he is surrounded by personal project that take a lot of dedication to bring to fruitition as many man "talk" of project but they stay embryonary projects forever (not that they don't want to do them, they can't find the motivation or the time).
If thing don't work out with you, i suspect he will simply go back to being single.
If you really still want him, do the counteroffer i mentioned. Do that offer "before" asking him the systematic reason why in his opinion the relationship failed (so that he will not think you said it because it was the reason he just mentioned, but that it was tought out in advance). If you don't make any offer, you lose him for good, if you don't ask him why it did not worked, you will never really know for sure. As he is introverted, you may have to offer him conversation paths that can allow him to open. Do not do that by texting, you need eye to ey contact. Take the whole thing with humor to not stress him because if he is tense he will be even more introverted at that moment. Just talk about how you are curious and like truth (that it hurt or not), that knowing this will help you in your future relation, anything that will give him a just reason to open up. If it is indeed a rountine problem, it also mean that is is an ego problem and that is not always easy to admid (so try to empathize with him that you are also a "little bit" like that so that he don't feel alone in this).