Learn English – “How could/can you do this to me?”

Insist is an intransitive verb. You can’t insist something or insist someone. You can only insist, and then say what it is you insist, using a clause beginning with that.

Want is a transitive verb. You can want something and even want someone. That’s why we can say I want you. That’s a complete sentence, but alone it means something rather intimate. That, however, isn’t the case when it’s followed by the plain form of the verb preceded by the particle to in your example.

In many contexts, both forms mean exactly the same. But I think #1 would occur more often.

1: I'm sorry for suspecting you.
Strongly implies you suspected someone was guilty of some specific misdeed.

2: I'm sorry for being suspicious of you.
May be used in contexts where you had more general misgivings about the moral character or motives of a person, though it can also (perhaps less commonly) be used in the same contexts as #1.

Another specific example of a difference; suppose you download and install updated video driver software on your computer, after which your computer keeps going wrong...

The driver is suspect (I think it contains bugs that are accidentally causing my problems).
The driver is suspicious (I think it contains malware that is deliberately harming my system).