What to think about people justifying ungenerous behavior by past people "taking advantage of them?"

Basically what's in the title. I'm reflecting on a past relationship that crawled, and the initial fight were everything began to go downhill was when he was reluctant to help me with a basic thing (storing my bike while I was away, plenty of space in his home) because of something that happened with someone else who kind of "took advantage of him being nice" (the person stored stuff and despite few messages later on, faded away).

Now, I still think, based on the time we spent together, it was a significant red flag for lack of generosity and resilience, and also that this past drama was not the end of the world. But from your point of view, what to think about people justifying half heartdness/self preservation in love all the time while saying they want to pursue you?