Can someone check my spanish paragraph.

Some of your sentences can lead to a misinterpretation. In order to elucidate, can you join the english text?

Honestly, the grammar is terrible. It may not be the case, but it looks as the result of some online translation machine.

En mi opinión, es importante que ustedes estén honesta con ustedes. (I don't understand. It reads: "In my opinión, it's important that you are (using "estar" instead of "ser) honest with you")
If it's "IMO, it's important that you be honest to each other", you should write: "En mi opinión, es importante que sean honestos uno con el otro".
If it's "IMO, it's important that you be honest with him/her", then you should write: "En mi opinión, es importante que seas honesta/o con él/ella".

Sugiero que ustedes no tengan miedo de lo que la otra persona piense de ustedes. Oscar, cuando le dijiste la verdad a tu esposa, la sorprendiste (you surprised her).
Es probable que ella se sienta mal por tener un affair (use the English word: but actually I don't know who had the affair: this is if she was the one; if it's otherwise: "Es probable que ella se sienta mal porque hayas tenido un affair.)

Yo creo que tú le duelas a ella. If this is supposed to mean "I think you hurt her", it's totally wrong. You wrote: "I think you would ache her, which makes no sense". I think you hurt her = "Creo que la heriste".

Sin embargo, tú le mentiste y tu esposa no está segura que de lo que dices sea cierto. Es urgente que le digas que la amas y la perdonas.
Sin embargo, Shelly, es necesario que tú hables con Oscar primero, antes de hacerlo con otro hombre. Por favor, no dudes de los sentimientos de Oscar. él te ama y quiera que ustedes sean felices.