- 僕がしたいって聞いたこと: =僕が「したい」と聞いたこと. Hmm this part is ambiguous because 聞く can mean both to ask and to hear. Either "the requests I heard from others" (someone else said したい) or "the things I asked for" (僕 himself said したい). Since you said it's in porn, perhaps this means the latter, but only you can determine which is correct.
- こんなにも: こんなに ("like this") + も (intensifier) → "this much"
叶えてくれようとしてくれてるんだもん is a colloquialism for 叶えてくれようとしてくれているのだもの. Yes lots of grammatical aspects are involved, so please refer to the links below.
- 叶えて: the te-form of 叶える ("fulfill", "grant")
- くれよう: the volitional form of the subsidiary verb くれる. ("for me")
- ~ようとする~ようとする: to try to do ~ ("to try to do ~ for me")
- ~ようとして: the te-form of the above ("trying to do ~ for me")
- くれて: the te-form of the subsidiary verb くれる
- る/いる: the subsidiary verb denoting an action in progressan action in progress ("is doing")
- んだもん/のだもの: "It's because ...", "Coz..."
- ん/の: explanatory-noexplanatory-no
- だ: the copula ("be")
- もん/もの: a sentence-end particle. See thisthis and this.
So put together, the sentence probably means "Cos you're trying to fulfill my wishes this much for me." It may mean "Cos you're trying to fulfill their wishes, which I heard from them, this much for me."
This sentence is not very well-written. You should not repeat くれる like this. This sentence should be either one of the followings:
- ~叶えようとしてくれてるんだもん Cos you're trying to fulfill for me...
- ~叶えてくれようとしてるんだもん Cos you're trying to fulfill for me...