Instead of "obosim", "obosi" is used which, I believe, is the "future presumptive" tense. Then, there are some other future tenses to learn; e.g., Alternatives 1 &2 (Future).
There is a "present presumptiv" (for which, much like the future, different patterns are in use) and there is a "past presumptive", but a "future presumptive" does not exist.
The formal pattern of the future in use here is built with the auxiliary vrea followed by an infinitive. In other words: obosi is an infinitive.
Thus obosi will stay the same if you change the person and number:
- Eu voi obosi - "I will get tired"
- Tu vei obosi - "You will get tired"
- Ei/ele vor obosi - "They will get tired" etc.
- Ea va сânta - "She will sing"
- Voi veți cânta - "You [plural] will sing" and so on