Inconsistency in Communication with Birth Father - What is going on?

Hi all, I've written here before about my experiences in being contacted by my birth father at 25 years old, and our bumpy reunion. Over the past year and a half, we got to a good place, communicating fairly frequently: texting with birth father about once a week, give or take, and also interacting with his wife, who I have also started to grow close to after a rocky start. The contact process happened very quickly at first and there was the common fallout from that, but we have moved beyond that and have been enjoying getting to know each other, including visits a couple times a year (we live in different states). I have a very busy career that kept me completely overwhelmed during the latter part of 2015, but we otherwise made efforts to see each other and communicate regularly. I visited birth dad and his family in March, staying there for a full week so that I could take more time to get to know and be comfortable with them. Too often with weekend or shorter visits, I would find the nerves and anxiety wearing off and some level of comfort being established right at the time the visit ended, so this week-long trip aimed to fix that issue. My birth dad has two younger kids with his ex-wife, and I also want to know them and have worked on developing that relationship in a way that feels natural and not too pushy (they're pre-teen and teen boy and girl, respectively). The March visit was very tumultuous for birth dad and his wife (the kids' step-mom) because they're going through lots of ups and downs that I imagine come with raising adolescents in a blended family. It was good to spend time but everyone was a bit distracted and I felt a little like I was not wanted there by him all the time. His wife is warm and made me feel welcome, but the environment was a little up and down. Overall good, but I do remember he and his wife both apologizing that it hadn't been the "ideal" visit. No worries, I know how it goes. I didn't hear from my birthdad after the visit at all, for over two months. No texts, nothing. I reached out to him after two months (swallowing my pride and fear that i had done something to make him angry, my confusion, etc.) and he didn't respond at first. I then texted his wife to ask if things were okay. She responded, and he responded to me shortly thereafter. He said it'd been "too long" since we'd talked and asked me how things were going, and we made small talk to catch up. That was mid-May. I have, again, not heard from him since that one short text message conversation. Father's Day came and went, and I spent it with my dad who raised me (since I was 6 months old), and I did not reach out to or hear from my birth father. I heard from his wife once, when she texted me sort of out of the blue and said things were very hectic there but that I was on her mind. And I've also heard once from my half-sister who is 15, which has been really lovely. But nothing from birth dad, who, it seems to me, should be the one I'm in most contact with. In the past when I have mentioned I haven't heard from him in a while (usually then just a couple weeks), he points out that I haven't talked to him either, sort of putting the ball back in my court. And I do understand that the relationship has to develop by both of us reciprocating contact, but I can't help that feel like even though I am an adult, in this situation I am still very much the child, and he should be putting in the effort to maintain consistent contact or at least reach out when there has been some distance. It is so hard for me to continually put myself out there and make myself vulnerable, and this had brought up feelings of abandonment that I didn't really realize I had. I was raised in a two-parent household and didn't even know about my birth dad until I was 15, so I am fortunate, I didn't grow up feeling abandoned or without a father. I am very loved and incredibly well cared for by my parents. But now that I have invested in exploring a relationship with my birth father and his family, these ups and downs are really destructive and make me feel like the floor is always shifting and like it will somehow end up being "my fault" because I did something wrong, or I did too much, or I didn't do enough. Has anyone else experienced this? I really don't know what to do next. It's entirely possible that they're just going through a lot there and that when things get hectic, I sort of drop from his priority list. But it isn't a good feeling, and I hate that I don't feel comfortable reaching out to him, but feel less nervous about texting his wife. I think that's probably just a difference in communication style, but I wish that I didn't feel so confused and I am genuinely interested in hearing suggestions about where to go from here.