Who is the subject of the sentence?


In the below I am unsure how to identify the subject (the one performing the
verbs) in the third sentence below. Originally I thought it was referring to
himself doing this, but in the line below he says その間も、俺は, which sounds to me
like the topic is switching to him. If the sentence above was describing his
actions then I'm not sure it would be necessary to state 俺は, which makes me
think it was referring to 心. Would anyone be able to clarify whether my
understanding is correct or what I am misunderstanding?

> キスを促すと、素直に唇を寄せてくる。
>
> 心は、よっぽどキスが好きなんだな。
>
> **舌を絡め、ぺちゃぺちゃ音をさせながら唾液をすすっていく。**
>
> その間も、俺は心の胸をまさぐり続けていた。




Unlike the first sentence, the third sentence has ていく, which almost certainly
indicates the subject is 俺. There is no subject switching in the fourth
sentence. (Of course 胸をまさぐる is something one can do while kissing.)

Grammatically speaking, it's not _necessary_ to say 俺は at all in the fourth
sentence. It's a bit hard to explain why it's there. For one, you can see the
fourth sentence is suddenly written in the past tense. The other three
sentences are in [historic
present](https://japanese.stackexchange.com/a/73870/5010) to enhance the
vividness of the description. This pattern feels like the fourth sentence is
written in a bit different mood, as if it is trying to "conclude" or "finish"
the whole scene. 俺は has been added explicitly to switch the mood, not the
subject; it would make the fourth sentence look slightly more objective and
less vivid.




Unlike the first sentence, the third sentence has ていく, which almost certainly
indicates the subject is 俺. There is no subject switching in the fourth
sentence. (Of course 胸をまさぐる is something one can do while kissing.)

Grammatically speaking, it's not _necessary_ to say 俺は at all in the fourth
sentence. It's a bit hard to explain why it's there. For one, you can see the
fourth sentence is suddenly written in the past tense. The other three
sentences are in [historic
present](https://japanese.stackexchange.com/a/73870/5010) to enhance the
vividness of the description. This pattern feels like the fourth sentence is
written in a bit different mood, as if it is trying to "conclude" or "finish"
the whole scene. 俺は has been added explicitly to switch the mood, not the
subject; it would make the fourth sentence look slightly more objective and
less vivid.

