Original version as submitted:
ã™ã‚“ã”ã„仲ã„ã„ã‹ã‚‰ã¦ã£ãã‚Šãã†ã ã¨ç”·ã£ã¦ãŸ.
---
I think this should be:
ã™ã‚“ã”ã„仲ã„ã„ã‹ã‚‰ã¦ã£ãã‚Šãã†ã ã¨æ€ã£ã¦ãŸ.
ç”· cannot be used as a verb, and in this sentence it is being used in the past progressive. ç”· looks a lot like æ€, which is a verb meaning to "think."
Romanized and corrected:
ã™ã‚“ã”ã„仲ã„ã„ã‹ã‚‰ã¦ã£ãã‚Šãã†ã ã¨æ€ã£ã¦ãŸ.
Su(n)goi naka ii kara, tekkiri so da to omotte(i)ta
(Our) relationship was very very close, so I clearly thought so.
---
Notes:
This is spoken Japanese written down, maybe manga dialogue or something. "SuNgoi" is a strong spoken emphasis of "sugoku."
We don't know for certain whose relationship is being talked about here: it might be between the speaker and another person being talked about, or it might be between two other people (i.e. not the speaker).
We don't know what the speaker "very clearly thought": it might be some detail about the person s/he's talking about or some event related to this person.