New Fiance- STD tests, any ideas?

We’ve met for only three months now, it been so great a relationship.I have always preferred to use condoms during love making as its still a new relationship, but my girl friend is slowly showing signs of disinterest. I am also scared about any possible STDs. Now I am thinking of discussing my worries and possible HIV testing for both of us in a clinic but uncertain how to start this chat.How about if she is unwilling to test in clinic, is there any home testing device for such purpose?We both live in Germany.
I will greatly appreciate all helpful inputs on this.

Thanks.

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